Serological discrimination between HTLV-I and HTLV-II antibodies by ELISA using synthetic peptides as antigens

Truncated MTA-1: a pitfall in ELISA-based immunoassay of HTLV-1 infection

HTLV-1 causes adult T-cell leukemia (ATL) and HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Recombinant envelope glycoprotein is used in production of diagnostic enzyme-linked immunosorbent assay (ELISA) kit. There are some reports that a significant percentage of Iranian HTLV-1 infected patients showed no seroreactivity with MTA-1 peptide, while HTLV-1 had been confirmed by PCR detection methods or ELISA kits containing a cocktail of HTLV-1 specific peptides. This report describes experiments designed to determine whether some discrepancies between ELISA and PCR results could be due to truncation of immunodominant epitopes using immunoassay method. We have cloned the MTA-1 epitope of env gene from HTLV-1 in NotI/NdeI sites of pET22b(+) expression vector. Sequencing analysis of recombinant plasmids revealed an insertion of a cytosine in position 271 causing a stop codon in the MTA-1 protein translation. SDS-PAGE analysis also failed to reveal the presence of the desired protein. Subjects with a mutant HTLV-1 env gene were shown to be seronegative using ELISA, but positive with PCR.

Chimeric synthetic peptides from the envelope (gp46) and the transmembrane (gp21) glycoproteins for the detection of antibodies to human T-cell leukemia virus type II

Two chimeric synthetic peptides incorporating immunodominant sequences from HTLV-II virus were synthesized. Monomeric peptides P2 and P3 represent sequences from transmembrane protein (gp21) and envelope protein (gp46) of the virus. The peptide P2 is a gp21 (370-396) sequence and the peptide P3 is a gp46 (178-205) sequence. Those peptides were arranged in a way that permits one to obtain different combinations of chimeric peptides (P2-GG-P3 and P3-GG-P2), separated by two glycine residues as spacer arms. The antigenic activity of these peptides was evaluated by UltramicroEnzyme-linked immunosorbent assay (UMELISA) by using panels anti-HTLV-II-positive sera (n = 11), anti-HTLV-I/II-positive sera (n = 2), HTLV-positive (untypeable) serum samples (n = 2), and anti-HTLV-I-positive sera (n = 22), while specificity was evaluated with anti-HIV-positive samples (n = 19) and samples from healthy blood donors (n = 30). The efficacy of the chimeric peptides in solid-phase immunoassays was compared with the monomeric peptides and a mixture of the monomeric peptides. Higher sensitivity was observed for chimeric peptide Q5 assay. Those results may be related to a higher peptide adsorption capacity to the solid surface and for epitope accessibility to the antibodies. This chimeric peptide would be very useful for HTLV-II diagnostic.

Assessment of a new immunoassay for serological confirmation and discrimination of human T-cell lymphotropic virus infections

The present study evaluated a new confirmatory assay for antibodies to human T-cell lymphotropic virus type 1 and 2 (HTLV-1 and HTLV-2) proteins performed with serum samples from various commercial sources. The new test is a line immunoassay (LIA) with a nylon membrane sensitized with the most relevant antigens of HTLVs: the envelope gp46 and gp21 as well as the gag p24 and p19 antigens, represented by either recombinant proteins or synthetic peptides. A total of 176 serum or plasma samples were tested, of which 66 were HTLV-1 positive, 72 were HTLV-2 positive, and 38 were HTLV negative; of the 38 HTLV-negative samples 23 were indeterminate by Western blotting (WB). Serially diluted samples (n = 33) from HTLV-1- and HTLV-2-infected patients were also analyzed to determine the sensitivity of the new assay. The new confirmatory assay (INNO-LIA HTLV) performed markedly better than WB assays for those samples reactive by screening. Accurate confirmation of the presence of HTLV-1 and HTLV-2 antibodies and accurate discrimination of HTLV-1 and HTLV-2 antibodies were obtained for all the HTLV-seropositive samples. Due to its enhanced specificity and sensitivity, the new assay not only improves the ability to confirm and discriminate HTLV infections but also eliminates the vast majority of WB-indeterminate and false-positive specimens.

An association of human T-cell lymphotropic virus type I infection with vascular dementia

Subjects ranging in age from 50 to 89 years old, either with or without dementia were studied by both ELISA for anti-human T-cell lymphotropic virus type I (HTLV-I) gag 100-130 antibody and by cranial CT in order to clarify the relationship between HTLV-I infection and dementia. The frequency of anti-HTLV-I antibody was found to be significantly higher in the patients with dementia (24/130, 18.5%) than in those without dementia (11/139, 7.9%) (P=0.0169). Among the various types of dementia, HTLV-I seropositivity was found to be significantly associated with vascular dementia (11/48, 23%) (P=0.0087), but not with Alzheimer type dementia. In addition, HTLV-I seropositivity was also associated with Babinski sign, and the severity of cerebral infarction, ventricular dilatation and periventricular lucency on CT. The presence of HTLV-I therefore appears to be one of the risk factors for vascular dementia in HTLV-I endemic areas.

HTLV-II-specific antisera raised in rabbits immunized with a synthetic peptide of HTLV-II envelope protein

In order to discriminate HTLV-II from HTLV-I, HTLV-II-specific polyclonal antibodies against a synthetic peptide of HTLV-II envelope sequence were raised in rabbits. We immunized two adult rabbits with a KLH-conjugated synthetic peptide corresponding to the amino acid sequence 171-196 of the HTLV-II envelope sequence, which is a specific region for HTLV-II as evaluated with an ELISA method. The resulting rabbit antisera to the synthetic peptide reacted with gp46 of HTLV-II lysates in Western blot analysis but not with that of HTLV-I. Flow cytometric analysis and immunohistochemical study revealed that these affinity purified antisera recognized some HTLV-II-producing cell lines examined, but not HTLV-I-producing cell lines or other cell lines uninfected by HTLV. These findings indicate that these antisera specifically recognized the envelope glycoprotein (gp46) of HTLV-II and suggest the specificity of this region in the immune response to HTLV-II. Such antisera are useful in distinguishing between HTLV-I and HTLV-II infection and in determining the presence of individual HTLV-II-infected cells both in vivo and in vitro, including non-lymphoid cells. They may also assist in the elucidation of the pathogenesis of HTLV-II.

Isolation and genomic analysis of human T lymphotropic virus type II from Ghana

An HTLV-II was isolated from a Ghanaian female patient with ARC and anti-HTLV-II antibody by cocultivation of PBMC with Molt-4 cells. A part of the 5' LTR of this virus was sequenced. Sequence homology between this virus and the corresponding sequence of Mo, the prototype of HTLV-II, is 97.4%. Furthermore, this virus is a member of the HTLV-IIa group, which was proposed by Hall et al. This is the first report of an HTLV-II sequence from Africa confirmed not only by serological evidence, but also by genomic analysis. This finding will provide useful information for considering the spread of HTLV-II in the world and the evolution of the HTLV group.

A novel monoclonal antibody specifically reactive with human T-lymphotropic virus type-II (HTLV-II) envelope protein

A novel monoclonal antibody (MAb), N5.4.4, specifically reactive with human T-lymphotropic virus type-II (HTLV-II) envelope glycoprotein (gp) has been developed through immunization with a synthetic peptide corresponding to the amino acid sequence 171-196 of the HTLV-II envelope protein (II-env 171-196). This MAb, which belonged to the IgG1 kappa subclass, reacted with the cytosmears of HTLV-II-infected cell lines (Si-IIA, CR-IIA-I and AS-IIA), but not with those of HTLV-I-infected cell lines (MT-1 and MT-2) or other HTLV-uninfected cell lines. On Western blot analysis, this MAb reacted with gp46 of HTLV-II lysates but not with HTLV-1 lysates. Moreover, flow-cytometric analysis revealed that this MAb recognized the native surface of only the HTLV-II-producing cells. Through application to immunohistochemical or serological method, this MAb may be of value in elucidating the pathogenesis of HTLV-II infection in comparison with HTLV-I.

HTLV-I, HIV-I, and hepatitis B and C viruses in Western Province, Papua New Guinea: a serological survey

Seven hundred and twenty-three serum samples from individuals in 13 Gidra-speaking villages in Western Province, Papua New Guinea were tested for evidence of infection with human T-lymphotropic virus type I (HTLV-I), human immunodeficiency virus type I (HIV-I), hepatitis B virus (HBV) and hepatitis C virus (HCV). No samples were positive for antibodies to HIV-I. Antibodies to HTLV-I were found in 13 samples (1.8%), HBV surface antigens (HBsAg) were found in 86 samples (11.9%), and antibodies to HCV were found in 30 samples (4.1%). Six (46.2%) of 13 HTLV-I positive samples were positive for HCV or HBsAg. The seropositive rate varied in different villages and the incidence of HTLV-I and HCV was higher in coastal and riverine areas than inland.

Discrimination between human T-cell lymphotropic virus type I and II (HTLV-I and HTLV-II) infections by using synthetic peptides representing an immunodominant region of the core protein (p19) of HTLV-I and HTLV-II

We describe enzyme immunoassays that use synthetic oligopeptides to discriminate serologically between human T-cell lymphotropic virus type I and II (HTLV-I and HTLV-II) infections. The peptides represented 20-amino acid segments between residues 111 and 130 (MA1) and residues 116 and 135 (MA2) of the p19 gag proteins of HTLV-I and HTLV-II, respectively. The assays were sensitive since 69 of 74 HTLV-positive sera were reactive to at least one of the two matrix (MA) peptides (sensitivity, 93.2%). By using the ratio of the optical density of MA1 to the optical density of MA2, which represents for every serum sample the ratio between the absorbance value obtained in the MA1 assay and the absorbance value obtained in the MA2 assay, 59 of the 69 reactive serum samples were clearly and easily typed as positive for either antibody to HTLV-I or antibody to HTLV-II. Eight of the 10 remaining reactive serum samples were analyzed further by an inhibition procedure, and their type specificities were then clearly identifiable. Therefore, the results indicate that all MA-reactive sera were serologically distinguished by our peptide assays.

Detection of antibodies to hepatitis C virus (HCV) structural proteins in anti-HCV-positive sera by an enzyme-linked immunosorbent assay using synthetic peptides as antigens

We have defined 10 linear immunogenic regions encoded by the putative hepatitis C virus (HCV) structural proteins (core and envelope) by employing an enzyme-linked immunosorbent assay (ELISA) and by using 17 sequential synthetic peptides covering the N-terminal 330 amino acids of the structural polyproteins as antigens. These peptides correspond to amino acids 1 to 24, 21 to 44, 42 to 68, 64 to 91, and 100 to 120 of the putative core protein and amino acids 192 to 212, 223 to 238, 236 to 258, 250 to 266, and 307 to 330 of the putative envelope protein. In particular, the peptide covering amino acids 21 to 44 of the core protein was reactive with all but one (40 of 41) of the serum samples giving a positive signal in the passive hemagglutination assay (PHA) using the core and nonstructural proteins (NS 3/4) of the virus as antigens. We detected the HCV genome in 25 (61%) of 41 PHA-positive serum samples by the polymerase chain reaction (PCR) test. Of 25 PCR-positive serum samples, 17 serum samples had reactivity to the peptides derived from the envelope protein. On the other hand, only 1 of the 16 PCR-negative serum samples had reactivity to the peptides derived from the envelope protein. Interestingly, we often observed high serum alanine aminotransferase levels in PCR-positive individuals bearing antibodies to the envelope protein.

Southernmost carriers of HTLV-I/II in the world

To clarify the real distribution of HTLV-I and -II carriers among indigenous people in central and South America, blood samples collected from indigenous people in isolated regions of Southern Chile were examined. Among 199 inhabitants from Chiloe Island and Pitrufquen town, three cases (1.5%) showed positive anti-HTLV-I antibodies. Two out of the three (82-year-old male and 58-year-old female) reacted to HTLV-II-specific Gag and/or Env proteins but not to HTLV-I-specific ones. The latter case was confirmed as an HTLV-II carrier by polymerase chain reaction test.